1. Field of the Invention
The present invention relates to a liquid crystal television receiver and a liquid crystal display apparatus including a liquid crystal panel for displaying video and a boosting circuit for lighting and driving a cold cathode tube used as a light source of a back light part for illuminating the liquid crystal panel from the back.
2. Description of the Related Art
In a television receiver using a liquid crystal panel as a display device, a gate driver 11 for driving a gate line of a liquid crystal panel 12 and a data driver (source driver) 14 for driving a data line (source line) of the liquid crystal panel 12 are provided in a liquid crystal display part 91 for displaying a video signal outputted from a receiving part 4 as shown in FIG. 5. Also, a first DC power source part 1 which is an AC adapter generates and sends out a first DC output 21 stabilized at 12 V. Also, a boosting circuit 19 of a back light part 5 is constructed so as to drive a cold cathode tube (not shown) using the first DC output 21 as an operating power source. Also, a second DC power source part 2 generates and sends out a second DC output 22 of 3.3 V required by the receiving part 4 etc. using an output 31a as an operating power source. Also, in the side of the liquid crystal display part 91, a DC output 23 of 12 V required by the data driver 14 is generated using a DC—DC converter 92 in which the second DC output 22 is used as an operating power source. Further, a DC output requested by the gate driver 11 is generated using a step-down circuit 93 or a charge-pomp circuit 94 (called a first conventional art).
As described above, in the first conventional art, the dedicated DC—DC converter 92, the step-down circuit 93 and the charge-pomp circuit 94 are provided in order to generate the DC output 23 used as an operating power source of the data driver 14. As a result of this, a configuration of a power source system becomes complicated and an increase in the number of parts or an increase in part cost is caused. A conventional art proposed to solve this problem will be described below (called a second conventional art). That is, in this art, a stabilized DC output sent out of a switching power source is supplied to a back light lighting control circuit as an operating power source and also is supplied to an output voltage control circuit for supplying a predetermined voltage of the fourth kind to a liquid crystal driving circuit as an operating power source. Therefore, there is no need to generate a DC output separately for the operating power source of the output voltage control circuit, and complication of the configuration of the power source system is avoided (for example, JP-A-9-50006).
However, in the case of using the second conventional art, a new problem arises and this problem will be described by applying a configuration of the second conventional art to a configuration of FIG. 5. That is, in the case of conforming to the configuration of the second conventional art, the first DC output 21 sent out of the first DC power source part 1 is guided to the boosting circuit 19 of the back light part 5 as an operating power source and also is guided to the data driver 14 as an operating power source. On the other hand, the data driver 14 drives the liquid crystal panel 12 by a signal corresponding to luminance of a pixel. Therefore, when a noise level included in the operating power source is large, due to the influence, variations in luminance due to the influence of noise occur in luminance of the liquid crystal panel 12 driven and a decrease in image quality is caused. In the meanwhile, the boosting circuit 19 forms a switching circuit having relatively large output electric power. As a result of this, a noise component caused by switching of the boosting circuit 19 tends to leak in the first DC output 21 and at the time when the noise component leaks in, the decrease in image quality described above was caused.